JP2000109863A - Lubricant for refrigerator using ammonia refrigerant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart an excellent compatibility with an ammonia refrigerant and an excellent stability to a lubricant by using a specified degree of unsaturation of a polyoxyalkylene type polyether as the lubricant. SOLUTION: As a lubricant for a refrigerator using an ammonia refrigerant, is used at least one of polyethers which are represented by the formula: X[- O-(AO)n-R]p [wherein X is a residue except a hydroxyl group from a monool or a polyol; (AO)n is a polyoxyalkylene group which is constituted by copolymerization of ethylene oxide with an at least 3C alkylene oxide; R is a hydrogen atom or a 1-4C alkyl group; (n) is an integer of at least 2; (p) is a valence of X], and which has 0.05 meq/g or below of a degree of its unsaturation. The kinematic viscosity of the polyether in the formula is preferably 15-200 cSt at 40 deg.C. A proportion of an oxyethylene group in (AO)n is preferably 50-10 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a lubricant for a refrigerator using ammonia as a refrigerant.

[0002]

2. Description of the Related Art Conventionally, a compression refrigerator comprises a compressor, a condenser, an expansion mechanism (expansion valve, etc.) and an evaporator, and its refrigerant is trichlorofluoromethane (R11), dichlorodifluoromethane (R12) or chlorofluoromethane. Chlorine-containing fluorocarbons (fluorocarbon compounds) such as difluoromethane (R22) have been used for a long time. These fluorocarbon compounds cause an international environmental problem of depletion of the ozone layer, the use of which is regulated, and chlorine-free difluoromethane (R32), tetrafluoroethane (R134)
Or R134a), difluoroethane (R152 or R134a).
152a) and the like. However, it has been pointed out that even these fluorocarbon compounds containing no chlorine have an extremely high global warming ability, and may cause environmental problems from a long-term perspective.

[0003] In recent years, hydrocarbons, ammonia and the like have attracted attention as refrigerants that do not cause such environmental problems. These refrigerants are far superior to the chlorofluorocarbon compounds in terms of environmental safety for the global environment and the human body. Further, although these compounds have not been the mainstream as refrigerants, they have been used for a long time.

Until now, since ammonia is not compatible with mineral oil, alkylbenzene, etc., which is a refrigerating machine oil, a refrigerating machine equipped with an oil circulating system at the compressor outlet side to separate and recover the oil and return it to the compressor inlet side again. It has been restricted to use only.
In addition, if the function of the oil circulation equipment is not sufficient, the refrigerating machine oil is taken out into the refrigerating cycle, causing a shortage of lubricating oil in the compressor. May be significantly shortened. Further, since the temperature of the evaporator is low, the high viscosity refrigerating machine oil taken out into the refrigeration cycle may remain in the evaporator and reduce the heat exchange efficiency. For this reason, refrigerators that use ammonia are relatively large and are limited to industrial equipment that can be regularly maintained.

However, in consideration of the above-mentioned environmental problems, ammonia refrigerants have been reviewed. Along with this, refrigerating machine oils that have compatibility with an ammonia refrigerant and do not require an oil circulation facility like a CFC refrigerant have been proposed. For example, EP 0490810 discloses a lubricant comprising a polyalkylene glycol which is a copolymer of ethylene oxide (EO) and propylene oxide (PO) and EO / PO = 4/1. Also, EP
585934 discloses a lubricant comprising a mono- or bifunctional polyalkylene glycol having EO / PO = 2/1 to 1/2. Furthermore, in DE 4404804, the general formula

Embedded image A polyether-based lubricant represented by RO— (EO) _x — (PO) _y —H (R is a C ₁ -C ₈ alkyl group, x = y = 5-55) is disclosed. . In EP 699737, the general formula

Embedded image Z ((CH ₂ CH (R ¹ ) O) _n- (CH ₂ CH)
(R ¹ ) O) _m ) _p- H (Z is C ₆ or more for an aryl group, C for an alkyl group
₁₀ or more, R ¹ is a hydrogen atom, a methyl group or an ethyl group, n =
A lubricant represented by 0 or a positive number, m = positive number, p = valence of Z) is disclosed.

Further, Japanese Patent Application Laid-Open No. 5-9483 and WO
No. 95/12594 discloses a refrigerating machine oil comprising a polyalkylene glycol diether and having excellent compatibility and stability with ammonia.

[0007]

When the above polyalkylene glycol-based compound is used as the refrigerating machine oil of an ammonia refrigerant refrigerator, the bifunctional polyalkylene glycol having two hydroxyl groups has stability and moisture absorption. It is pointed out that there is a problem with sex. Further, the above polyalkylene glycol diether has a problem that it has lower compatibility with ammonia than polyalkylene glycol having a hydroxyl group, and is incompatible depending on the structure. In addition, polyalkylene glycol diether has the terminal of the molecule blocked with an alkyl group,
There was a disadvantage that the production process became complicated due to the end blocking.

[0008] Accordingly, an object of the present invention is to provide a refrigerating machine oil for a refrigerating machine that uses ammonia as a refrigerant having excellent compatibility with an ammonia refrigerant and excellent lubricity and stability.

[0009]

That is, the present invention provides the following general formula (1):

X ｛—O— (AO) _n —R｝ _p (1) wherein X represents a residue obtained by removing a hydroxyl group from a monool or a polyol, and (AO) _n represents ethylene oxide and the number of carbon atoms. R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and n represents 2 or more, a polyoxyalkylene group formed by copolymerization of three or more alkylene oxides.
P represents the valence of X. At least a polyether represented by the formula:
It is a lubricant for a refrigerator using an ammonia refrigerant of not more than 05 meq / g.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the general formula (1), X represents a residue obtained by removing a hydroxyl group from a monol or a polyol. As the monol, for example, methanol, ethanol, propanol, 2-propanol, butanol,
2-butanol, pentanol, 2-pentanol, 3
-Pentanol, isopentyl alcohol, 2-methyl-4-pentanol, hexanol, secondary hexanol, isohexanol, heptanol, secondary heptanol, octanol, 2-ethylhexanol, secondary octanol, isooctanol, nonanol, secondary Nonanol, 1-decanol, isodecyl alcohol, secondary decanol, undecanol, secondary undecanol, 2-
Methyldecanol, lauryl alcohol, secondary dodecanol, 1-tridecanol, isotridecyl alcohol, secondary tridecanol, myristyl alcohol, secondary tetradecanol, pentadecanol, secondary pentadecanol, cetyl alcohol, palmityl alcohol, 2
Grade hexadecanol, heptadecanol, secondary heptadecanol, stearyl alcohol, isostearyl alcohol, secondary octadecyl alcohol, oleyl alcohol, behenyl alcohol, eicosanol, docosanol, tetracosanol, hexacosanol, octacosanol, myricyl alcohol, Lasserol, tetratriacontanol, allyl alcohol, cyclopentanol, cyclohexanol, 2-butyloctanol, 2-butyldecanol, 2-hexyloctanol, 2-hexyldecanol, 2-hexyldecanol, 2-octyldecanol, 2-octyldodecanol, 2-octyltetradecanol, 2-decyldodecanol, 2-decyltetradecanol, 2-decylhexadecanol, 2-do Siltetradecanol, 2-dodecylhexadecanol, 2-dodecyloctadecanol, 2-tetradecyloctadecanol, 2-tetradecylicosanol, 2-hexadecyloctadecanol, 2-hexadecylicosanol Alcohols such as phenol, cresol, ethylphenol, tert-butylphenol, hexylphenol, octylphenol, nonylphenol, decylphenol, undecylphenol, dodecylphenol, tridecylphenol, tetradecylphenol, phenylphenol, benzylphenol, styrenated phenol, p-
Phenols such as cumylphenol are exemplified.

As the polyol, for example, ethylene glycol, propylene glycol, 1,4-butanediol, 1,2-butanediol, neopentyl glycol, 1,6-hexanediol, 1,2-octanediol, 1,8- Octanediol, isoprene glycol, 3-methyl-1,5-pentanediol, sorbite, catechol, resorcin, hydroquinone, bisphenol A, bisphenol F, hydrogenated bisphenol A,
Diols such as hydrogenated bisphenol F and dimer diol; glycerin, trioxyisobutane, 1,2,3-
Butanetriol, 1,2,3-pentanetriol,
2-methyl-1,2,3-propanetriol, 2-methyl-2,3,4-butanetriol, 2-ethyl-
1,2,3-butanetriol, 2,3,4-pentanetriol, 2,3,4-hexanetriol, 4-propyl-3,4,5-heptanetriol, 2,4-dimethyl-2,3 Trihydric alcohols such as 4-pentanetriol, pentamethylglycerin, pentaglycerin, 1,2,4-butanetriol, 1,2,4-pentanetriol, trimethylolethane and trimethylolpropane; pentaerythritol, erythritol,
2,3,4-pentane tetrol, 2,3,4,5-hexane tetrol, 1,2,4,5-pentane tetrol, 1,3,4,5-hexane tetrol, diglycerin, sorbitan Pentahydric alcohols such as adonitol, arabitol, xylitol and triglycerin; hexahydric alcohols such as dipentaerythritol, sorbitol, mannitol, iditol, inositol, darcitol, talose and allose; Examples thereof include polyglycerin and dehydration condensates thereof. p is a valence of X, and a number of 1 to 8 is preferable.

X may be a residue of a compound derived from the above monol or polyol. Examples of such a compound include sodium alcoholate and potassium alcoholate of the above-mentioned monol or polyol.

Of these, if the valence p of X is too large, the molecular weight of the obtained polyether becomes too large, the viscosity becomes too high, or the compatibility with the ammonia refrigerant is lowered. p is more preferably 1 to 3. In particular, it is most preferable that p is 1, that is, X is a residue obtained by removing a hydroxyl group from a monol. Even if it is a monol, the carbon number of X is preferably 1 to 8, more preferably 1 to 4, since the compatibility with the ammonia refrigerant may decrease when the carbon number is too large. Preferably X is a methyl group.

In the general formula (1), (AO) _n
Represents a polyoxyalkylene group formed by copolymerization of ethylene oxide and an alkylene oxide having 3 or more carbon atoms. Examples of the alkylene oxide having 3 or more carbon atoms include propylene oxide, butylene oxide, α-olefin oxide, styrene oxide and the like. The polymerization ratio of ethylene oxide and alkylene oxide having 3 or more carbon atoms is not particularly limited,
In order to impart excellent compatibility with ammonia to the polyether, which is a polymerization product, at least ethylene oxide is required. However, if the proportion of ethylene oxide increases too much, the low-temperature properties such as hygroscopicity and pour point may deteriorate, or a powdery solid may precipitate or precipitate, so oxyethylene in (AO) _n The ratio of the group is preferably 50% by weight or less, and 50 to 10% by weight.
Is more preferable, and 30 to 10% by weight is most preferable. For the same reason, the ratio of the number of oxyethylene groups in the molecule of the polyether represented by the general formula (1) used in the present invention is 40% or less based on the total number of oxyalkylene groups. Is preferably 30% or less, and most preferably 20% or less.

The form of the copolymerization may be block polymerization, random polymerization or a mixture of block polymerization and random polymerization, but the (AO) _n portion is a polyoxyalkylene chain in which all of the blocks are formed by block polymerization. And (AO) _n are preferably a polyoxyalkylene chain formed by random polymerization or a polyoxyalkylene chain partially containing random polymerization. n represents a number of 2 or more, preferably 2 to 150, and more preferably 5 to 100.

In the general formula (1), R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. R is preferably a hydrogen atom or a methyl group. When R is an alkyl group, the compatibility of the polyether represented by the general formula (1) with ammonia is generally slightly lower than that in which R is a hydroxyl group, but is excellent in stability.

The polyether represented by the general formula (1) used in the present invention must have a degree of unsaturation of 0.05 meq / g or less. Further, it is preferably at most 0.04 meq / g, more preferably at most 0.03 meq / g, most preferably at most 0.02 meq / g. This is because when producing a polyether represented by the general formula (1) containing an oxypropylene group and used in the present invention, propylene oxide may cause a side reaction to generate an allyl group. When formed, the thermal stability of the lubricant itself first decreases. In addition, it forms a polymer and causes sludge, and is liable to be oxidized, thereby generating peroxide. When the peroxide is generated, it is decomposed to generate a carbonyl group, which reacts with the ammonia refrigerant to generate an acid amide, which also causes clogging of the capillary.

The peroxide value is 10.0 meq / kg
Or less, more preferably 5.0 meq / kg or less, and most preferably 1.0 meq / kg or less. The carbonyl value is 100 weight p
pm or less, more preferably 50 ppm by weight or less, most preferably 20 ppm by weight or less.

In order to produce the polyether represented by the general formula (1) having a low degree of unsaturation, the reaction temperature at the time of reacting propylene oxide is preferably 120 ° C. or lower, more preferably 110 ° C. It is better to do the following. In addition, if an alkaline catalyst is used in the production, an inorganic adsorbent such as activated carbon, activated clay, bentonite, dolomite,
When an aluminosilicate or the like is used, the degree of unsaturation can be reduced. In producing the lubricant of the present invention,
Alternatively, contact with oxygen as much as possible or using an antioxidant together can also prevent an increase in peroxide value or carbonyl value.

The degree of unsaturation, peroxide value and carbonyl value are values measured by a standard oil and fat analysis test established by the Japan Oil Chemists' Society. The outline of the measuring method is shown below. <Method of measuring the degree of unsaturation (meq / g)> A whis solution (ICl-acetic acid solution) was allowed to react with the sample, and the sample was allowed to stand in a dark place. The iodine value was calculated by titration with, and the iodine value was converted to a vinyl equivalent, which was defined as the degree of unsaturation. <Measurement method of peroxide value (meq / kg)> Potassium iodide was added to a sample, the generated free iodine was titrated with sodium thiosulfate, and this free iodine was converted to the number of milliequivalents per 1 kg of the sample. The oxide value was used. <Method for measuring carbonyl value (ppm by weight)>
4-Dinitrophenylhydrazine was allowed to act to generate a chromogenic quinoid ion, the absorbance of this sample at 480 nm was measured, and the carbonyl amount was converted to a carbonyl amount based on a calibration curve previously determined using cinnamaldehyde as a standard substance.

The lubricant of the present invention is a polyether represented by the general formula (1) which satisfies the above conditions, and when R is a hydrogen atom, is a compound in which the structural terminal on the opposite side of X is a hydroxyl group. . In the polyether represented by the general formula (1) used in the present invention, the number of secondary hydroxyl groups of the hydroxyl group located at the terminal of the structure is 50% of the total number of hydroxyl groups.
It is preferably at least 70%, more preferably at least 70%, most preferably at least 80%. This is because when 50% or more of the hydroxyl groups located at the terminal of the structure are secondary hydroxyl groups, they exhibit excellent stability to ammonia refrigerant.

That is, in general, when a hydroxyl group bonded to a primary carbon atom undergoes oxidation, it changes to a carboxylic acid via an aldehyde. However, in the presence of ammonia, the carboxylic acid may form an acid amide, which may precipitate. is there. On the other hand, the hydroxyl group bonded to the secondary carbon atom undergoes oxidation only to change to a ketone, and the ketone is more stable than the carboxylic acid in the presence of ammonia. In addition, the secondary hydroxyl group is a hydroxyl group bonded to a secondary carbon atom.

The molecular weight of the polyether represented by the general formula (1) used in the present invention is not particularly limited, but the molecular weight and the viscosity tend to be proportional. , Molecular weight 300-3.0
About 00 is preferable.

The kinematic viscosity of the polyether represented by the general formula (1) used in the present invention is not particularly limited. However, if the viscosity is too low, the sealing property is poor and the lubricating performance may be reduced. The compatibility with ammonia decreases, and the energy efficiency also deteriorates. Therefore, the kinematic viscosity at 40 ° C. is preferably 15 to 200 cSt, and more preferably 20 to 150 cSt.

Ammonia, which is a refrigerant, and the lubricant of the present invention are preferably used in a weight ratio of 99/1 to 1/99 from the viewpoint of cooling ability of the refrigerant and sealing property of the lubricant. More preferably, it is used in the range of / 5 to 30/70.

Since the polyether represented by the general formula (1) used in the present invention is a lubricant used in a refrigerator for ammonia refrigerant, it is preferable that impurities such as moisture and chlorine are as small as possible. Moisture promotes deterioration of lubricants, additives, etc., so the smaller the better, the better, preferably 500 ppm or less, more preferably 300 ppm or less, 100 pp
m or less is most preferable. In general, since polyether has hygroscopicity, caution is required during storage or filling in a refrigerator. However, polyether can be removed by distillation under reduced pressure or by passing through a dryer filled with a desiccant.

When the polyether represented by the general formula (1) used in the present invention wherein R is an alkyl group having 1 to 4 carbon atoms, a compound containing chlorine such as methyl chloride is used as a starting material. However, since chlorine forms an ammonium salt in the presence of ammonia and causes clogging of the capillary, the chlorine content is preferably as small as possible, preferably 100 ppm or less, more preferably 50 ppm or less.

The method for producing the polyether represented by the general formula (1) used in the present invention is not particularly limited, and may be a conventional method for producing a polyether. For example, a mixed alkylene oxide of ethylene oxide and an alkylene oxide having 3 or more carbon atoms (for example, propylene oxide) is added to an alcohol such as methanol as a starting material in the presence of an alkali catalyst such as sodium hydroxide or potassium hydroxide. 100-150 ° C, pressure 0-10kg
/ Cm ² .

Other components can be added to the lubricant of the present invention as needed. For example, known refrigerator lubricants such as mineral oil, alkylbenzene, polyalkylene glycol diether, polyalkylene glycol, and polyol ester; and extreme pressure agents such as tricresyl phosphate and triphenyl phosphate; Antioxidants such as ributyl-4-methylphenol, 4,4'-methylenebis-2,6-di-tert-butylphenol, dioctyldiphenylamine, dioctyl-p-phenylenediamine; stabilizers such as phenylglycidyl ether; glycerin mono Additives such as oily agents such as oleyl ether and glycerin monolauryl ether; metal deactivators such as benzotriazole; and foam control agents such as polydimethylsiloxane can be appropriately added. Further, additives such as a detergent / dispersant, a viscosity index improver, a rust inhibitor, a corrosion inhibitor, a pour point depressant and the like can be blended as required. These additives are generally added in an amount of about 0.01 to 10% by weight based on the lubricant of the present invention.

[0030]

The present invention will be described more specifically with reference to the following examples. In the following examples, “parts” and “%” are based on weight unless otherwise specified. Further, EO is an abbreviation of an oxyethylene group and PO is an abbreviation of an oxypropylene group, and the symbol “−” between them represents a block copolymer,
“/” Represents random copolymerization. The following tests were performed for each of the examples and comparative examples, and the lubricants were evaluated as lubricants for refrigerators using an ammonia refrigerant.

(Production Example) In a 3-liter autoclave, 64 g of methanol and 8 g of potassium hydroxide as a catalyst were placed.
Was charged. After dissolving the catalyst, the reaction temperature is 100 to 150 ° C,
At a pressure of 0 to 10 kg / cm ² , 1,548 g of propylene oxide and 388 g of ethylene oxide (weight ratio of 8
/ 2) were reacted. After aging, reaction temperature 100-150 ° C, pressure 0-10kg / c
At m ² , 200 g of propylene oxide was reacted to obtain a lubricant of Example 1. The lubricants of other examples and comparative examples were produced in the same manner. The degree of unsaturation of each sample was measured by the method described above.

<Compatibility with Ammonia> After 5 ml of each sample and 1 ml of ammonia were sealed in a glass tube, they were cooled from room temperature at a rate of 1 ° C./min, and the temperature at which two layers were separated was measured. <Falex baking load> In order to evaluate the lubricity of each sample, the Falex baking load was measured in accordance with ASTM-D-3233-73. <Bomb test> The following tests were performed to evaluate the stability of each sample in an ammonia atmosphere. That is,
300m loaded with iron wire of 1.6mm diameter as catalyst
50 g of each sample was placed in a 1-liter cylinder, pressurized with ammonia to 0.6 kg / cm ² G, and further charged with nitrogen gas.
The pressure was increased to 7 kg / cm ² G. Thereafter, the mixture was heated to 150 ° C. and kept at the same temperature for 7 days. Thereafter, the sample was allowed to cool to room temperature, the pressure was reduced by removing gas, and the pressure was further reduced to remove ammonia from the sample. The total acid value and hue of the sample thus obtained were measured. After the test, the sample was transferred to a 100 ml beaker and left at room temperature for 5 hours.
Changes in appearance were visually observed and evaluated according to the following ratings. Table 1 shows the obtained results. 0: No abnormality (same state as before test). 1: Slight powdery precipitate is seen at the bottom of the beaker. 2: State between score 1 and 3. 3: A powdery precipitate is found on the entire bottom surface of the beaker. 4: Solidification or fluidity at room temperature was lost.

[0033]

[Table 1]

In Table 1, {(PO) / (EO)} represents a random copolymer of propylene oxide and ethylene oxide. G represents a residue obtained by removing a hydroxyl group from glycerin. In addition, when the water content of each sample was measured using a Karl Fischer moisture meter, it was 300 p
pm or less. Further, when the peroxide value and carbonyl value of each sample were measured by the above-mentioned method, the peroxide value was 2.5 meq / kg to 3.2 meq / kg, and the carbonyl value was 10 ppm to 15 ppm by weight. The symbol * represents the weight ratio of {(PO) / (EO)}. However, for Example 7 and Comparative Example 5, the (PO) / (EO) ratio for the whole is shown.

[0035]

The effect of the present invention is to provide a refrigerating machine oil for a refrigerating machine which uses ammonia as a refrigerant having excellent compatibility with an ammonia refrigerant and excellent lubricity and stability.

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) C10N 40:30 (72) Inventor Goro 7-35 Higashiogu, Arakawa-ku, Tokyo Asahi Denka Kogyo Co., Ltd. ( 72) Inventor Takashi Kaimai 3-17-35 Niisonaminami, Toda City, Saitama Prefecture Japan Energy Co., Ltd. (72) Inventor Hitoshi Takahashi 3-17-35 Niisonanami, Toda City, Saitama Prefecture Japan Energy Co., Ltd.

Claims (5)

[Claims] 1. A compound represented by the following general formula (1): X ｛—O— (AO) _n —R｝ _p (1) wherein X is a residue obtained by removing a hydroxyl group from a monool or a polyol. Wherein (AO) _n represents a polyoxyalkylene group formed by copolymerization of ethylene oxide and an alkylene oxide having 3 or more carbon atoms, R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and n represents 2
P represents the valence of X. ] A lubricant for a refrigerator using an ammonia refrigerant, wherein the lubricant has at least one kind of polyether represented by the formula: and an unsaturation degree of 0.05 meq / g or less. (AO) _n is a polyoxyalkylene group formed by random copolymerization of ethylene oxide and propylene oxide and / or butylene oxide or a polyoxyalkylene group partially containing a random copolymer. The lubricant for a refrigerator according to claim 1. 3. The refrigerator lubricant according to claim 1, wherein the polyether represented by the general formula (1) has a kinematic viscosity at 40 ° C. of 15 to 200 cSt. 4. The refrigerator lubricant according to claim 1, wherein the proportion of oxyethylene groups in (AO) _n is 50 to 10% by weight. 5. R is a hydrogen atom, and the number of secondary hydroxyl groups is at least 50% of the total number of hydroxyl groups located at the structural end of the polyether represented by the general formula (1). The lubricant for a refrigerator according to any one of claims 1 to 4.